1. Field of Invention
The invention relates generally to wireless communication and more particularly to methods to hand off a wireless client between access points.
2. Discussion of Related Art
Voice over IP, or VoIP, is a system for routing voice conversations over an electronic network based on the Internet Protocol (or IP). Most commonly, VoIP conversations are routed over the Internet itself, although they may be routed on any IP-based network. VoIP has advantages over traditional analog voice communications, including reduced cost and the ability to move a VoIP phone number to various locations.
VoIP generally depends on an uninterrupted network connection. If packets carrying voice information are lost or delayed, it may be difficult to sustain a conversation. Many other forms of IP communication similarly require a high quality of service. Examples include videoconferencing as well as streaming video and audio.
IEEE 802.11 is a set of wireless network standards that is now common. Large scale 802.11 wireless networks with multiple access points (or APs) have recently been deployed in university campuses, office buildings, airport terminals, and other public and private venues. Many places around the world (such as San Francisco, Philadelphia, Paris, and Taipei) have developed plans to roll out city-wide 802.11 coverage. When a wireless client moves out of range from one access point and into the range of another access point, the connection must be “handed off” between the APs for the client to remain connected to the network. The standard 802.11 procedure for handing off a wireless client between access points, however, often incurs a significant delay. This delay is typically on the magnitude of hundreds of milliseconds to several seconds, depending on the software and hardware configurations and operation mode of the network(s) involved.
During this handoff period, data service must be temporarily disrupted. This interruption of service can result in a gap in delay-sensitive applications such as VoIP, videoconferencing, streaming media, and video games. A silent gap may be unacceptable to any delay-sensitive applications.